The present invention relates to electronically controlled fuel injection for internal combustion engines, and more particularly to a system for electronically controlling fuel injection on the basis of the charging and discharging of a capacitor.
As a system for controlling fuel injection into an internal combustion engine is well known an electronically controlled fuel injection system wherein the fuel injection quantity to be injected into the engine is controlled in accordance with engine operating parameters including intake air quantity. It is important for such a system to immediately and accurately respond to the fuel injection quantity requirements under varying engine operating conditions. However, when particularly performing the control of fuel injection quantity independently for each cylinder of a multi-cylinder engine, the problem of responsibility is encountered as a result of converting the amount of intake air to a corresponding digital signal to compute the fuel injection quantity by a microcomputer or the like.
Attempts to avoid the problem noted above have been made hitherto, such a technique being disclosed in Japanese Pat. No. 55-36814, in which a basic injection time period is determined so as to be equal to a discharging time period of a capacitor, the capacitor being charged by a constant current and the discharging current being determined as a function of intake air quantity. However, the prior art system does not still produce satisfactory results, since the system is arranged such that the basic injection pulse signal is generated in response to a predetermined crank angular position. Namely, to perform the control of fuel injection amount independently for each cylinder, it is required that the fuel injection is terminated before a piston reaches a top dead center (i.e. an angle greater than BTDC 5.degree. or so) which is the start position of intake stroke of the cylinder in view of blow-by of injected fuel caused by valve overlap. However, the basic injection quantity is determined in response to the charging and discharging actions performed with respect to a predetermined crank angle, and therefore this results in the difficulty to control the termination timing of fuel injection in accordance with engine operating conditions.